Question

How do you solve `2cos2x + 1 = 0`?

Answer 1

Solve 2cos 2x + 1 = 0

Ans: `+- pi/3`

Explanation:

2cos 2x = -1
`cos 2x = - 1/2` --> `2x = +- (2pi)/3` --> `x = +- pi/3`
Check by calculator.
`x = pi/3` --> `2x = ((2pi)/3)`--> `cos 2x = - 1/2` --> cos 2x + 1 = 0. OK